1. Field of the Invention
The present invention relates to a system for automatically preparing a numerical control program which is used to control a cutting machine tool with, preferably, an automatic tool changer. More particularly, it relates to such a system capable of automatically preparing a numerical control program used in machining a workpiece, based upon machining information on a plurality of portions of the workpiece.
2. Discussion of the Prior Art
Known numerical controllers for cutting machine tools such as machining center are provided with an automatic programming function. In such an automatic programming function, a numerical control program used in successively machining a plurality of portions on a workpiece is automatically prepared based upon machining information which is input to define a machining position and a machining shape for each of the workpiece portions.
One type of the known numerical controllers is designed to automatically determine the machining order of the workpiece portions in such a manner as to follow the order in which machining information for the workpiece portions are input. Another type of the known numerical controllers is designed to automatically determine the machining order of the workpiece portions in such a manner as to make the number of tool change operations minimum.
However, in these known numerical controllers, the machining order is determined without taking into consideration a machining accuracy required for each workpiece portion. Thus, in the case that drillings have to be performed at respective positions P1-P4 close to a bore Ha needing a high precision boring, as shown in FIGS. 12(a) and 12(b), a numerical control program prepared automatically by the known controllers would instruct that a finish or fine boring for the bore Ha be performed in advance of the drillings at the positions P1-P4. This gives rise to a problem that the finish accuracy of the bore Ha is deteriorated as a result of being subjected to stress and/or being damaged or scratched with chips during drilling operations of the holes Hb-He.